Since your center needs to match your mains/ fronts...what speakers are you using for your front l/r? The builder Should be able to tell you the brands. Most AV experts would recommend against in ceiling speakers, unless these have enclosure or you really like thesound in an elevator!
How big is the room the tv is in? And what type of budget do you have? Klipsch may make thebest budget subwoofers, but I WOULD NOT mix horns with regular tweeters for your center.

Since your center needs to match your mains/ fronts...what speakers are you using for your front l/r? The builder Should be able to tell you the brands. Most AV experts would recommend against in ceiling speakers, unless these have enclosure or you really like thesound in an elevator!
How big is the room the tv is in? And what type of budget do you have? Klipsch may make thebest budget subwoofers, but I WOULD NOT mix horns with regular tweeters for your center.

Thanks for replying - the ceiling spreakers actually sound quite good - not boxy at all.
The TV room is pretty big - it's an open area with family room/kitchen/eat-in area - probably 21' x 35', but the main watching/listening area is near the center.
When you say you would not mix horns/tweeters, are you referring to the Klipsch?

I suggest that you look at the Cambridge Audio S50 center speaker, which is only 4.6 inches tall.

It has excellent sound quality, and runs around $200.

The subwoofer depends on what you want to spend.

I use the NHT B12D, which is an excellent one, for $700.

The Klipsch RW12D runs around $450 or so, and it is very good.

For around $250, you can get the Polk PSW505, which is probably the best you can get for a low-budget price.

Sound bars mostly suck pretty bad.

Thanks - I'll check into your suggestions.
I've heard a lot of people say that soundbars aren't very good - mind you, I'm not looking for high-end stuff (clearly) but I can't stand crappy sound either.
I'd say my biggest issue is trouble understanding the voice track in movies - sometimes they mumble (others in the same movie are clear) but sometimes
the whole soundtrack can be thick and mushy...

Any comment on the Klipsch SB-1 - or does it fall in to the 'sucks' category?

Thanks - I'll check into your suggestions.
I've heard a lot of people say that soundbars aren't very good - mind you, I'm not looking for high-end stuff (clearly) but I can't stand crappy sound either.
I'd say my biggest issue is trouble understanding the voice track in movies - sometimes they mumble (others in the same movie are clear) but sometimes
the whole soundtrack can be thick and mushy...

Any comment on the Klipsch SB-1 - or does it fall in to the 'sucks' category?

What brand and model are your in-ceiling speakers? I would not spend a pile of money on a soundbar.

If it was me, I would consider replacing those in-ceiling speakers you have (chances are they are some cheap builder grade speaker, but you might be able to confirm if you pull the grill off one and send us a picture) with a couple options:

Yes, klipsch speakers have horn tweeters, which don't play well with traditional dome tweeters.
If you are having trouble hearing dialogue in movies, I highly doubt those speakers are the "right nan for the job"! I agree, get a decent set of bookshelves, matching center and the best sub you can afford (I got the klipsch rd-12 for 280 recently... Not as good as the svs, nht or outlaw subs, but not 500+ dollars either). Use the in ceiling surrounds and you will have a pretty good system.
I just don't think in ceiling speakers can do it for that space...